1. Field of the Invention
The present invention relates to environmental control systems, and particularly to systems that provide controlled temperature and humidity environments for airborne payloads.
2. Discussion of the Known Art
Airborne reconnaissance, surveillance, and electronics payloads are typically mounted in an unpressurized equipment bay on an aircraft, and are expected to operate reliably at altitudes from sea level to 60,000 feet or higher above mean sea level. Such payloads often include precision optics, focal plane arrays, and electronics. The electronic equipment may include recorders, data links, sensor control units, control electronics units, and countermeasures systems.
The performance of optical system components is affected greatly by thermal expansion and contraction. Additionally, opto-mechanical and electronic components that are integrated within precision optical systems are also sensitive to temperature and moisture. Thus, in order for precision optical system payloads to operate properly and accurately over a given aircraft mission flight profile, the temperature and the humidity inside the equipment bay must be controlled according to the specifications imposed by the system payloads. The temperature requirements are typically 25 deg. C.+/−2 deg. C., without condensation developing inside the bay throughout the mission flight profile. Depending on the application, the internal equipment bay temperature specification can range between −30 deg. C. to 40 deg. C., with a set temperature within this band controlled to a tolerance of +/−5 deg. C. to +/−1 deg. C. throughout the flight profile.
At present, either an air cycle machine (ACM) or a vapor cycle machine (VCM) and associated fans are used for thermal control of electronics and imaging systems aboard aircraft. Airborne ACM systems are disclosed, for example, in U.S. Pat. No. 6,058,715 (May 9, 2000) and U.S. Pat. No. 6,427,471 (Aug. 6, 2002), and in U.S. Patent Application Pubs. No. 2006/0059942 (Mar. 23, 2006) and No. 2008/0022688 (Jan. 31, 2008). Airborne VCM systems are described, e.g., in U.S. Pat. No. 5,918,472 (Jul. 6, 1999), and in U.S. Patent Application Pub. No. 2008/0199326 (Aug. 21, 2008). Disadvantages of either system are that the ACM and the VCM machines each weigh approximately 100 pounds and consume a large amount of electrical power and critical volume aboard an aircraft. Also, the cost of either system typically exceeds $100,000, with a mean-time-between-failures (MTBF) of only about 4,000 flight-hours.
Cyclone separators that remove dust, liquid, and other matter from a supply of air are generally known. Cyclone separators operate by directing the supplied air to flow in a conical path, thereby causing matter carried or entrained within the air to separate from the air by centrifugal force. A cyclone separator for dehumidifying compressed air for marine control equipment is disclosed in U.S. Pat. No. 6,019,822 (Feb. 1, 2000) which is incorporated by reference. See also, U.S. Pat. No. 6,851,459 (Feb. 8, 2005); U.S. Pat. No. 7,381,235 (Jun. 3, 2008); and U.S. Pat. No. 7,594,941 (Sep. 29, 2009), all of which are also incorporated by reference. As far as is known, however, cyclone separators have not been used in systems for controlling the thermal environment of sensitive airborne payloads.
Accordingly, there is a need for a reliable and light weight environmental control system for sensitive airborne payloads, particularly a system that consumes minimal space and electrical power aboard an aircraft, and which can be constructed and maintained at relatively low cost.